Why Are Constellations Useful for Mapping the Sky?

Tracking the Seasons

• By locating the position of a constellation at a particular time of year, ancient societies were able to know when to plant and when to harvest. Using constellations in this way made agriculture more reliable, facilitating the ability of man to move away from hunter-gathering and toward farming. It is thought that monuments such as Stonehenge in England and even the Pyramids of Egypt were used in this way to predict the changing seasons depending on where a constellation appeared in the sky.

Navigating

• Before the advent of global positioning satellites, sailors used a sextant to find their location at sea. By measuring the angle between the sun and the horizon, a sailor would be able to accurately determine his position. At night a navigator can pick one of 57 celestial objects to use as an aide in setting the ship's course. By knowing the constellations, he or she can easily locate and identify the correct star from a sky containing tens of thousands of stars.

New Discoveries

• Today constellations can be used to easily identify new discoveries in the cosmos. Professional and amateur astronomers alike will know instantly which part of the sky to train their instruments on just by knowing the constellation where any new discovery is made. They can then use a star within the constellation to serve as a signpost to accurately locate new objects. This is particularly important for short-lived events, such as Super Novae, or for identifying objects near the earth, such as previously unseen meteors.

Naming

• Johann Bayer introduced the first naming convention for stars in 1603. This classification follows the Greek alphabet with the brightest star in a constellation given the identifier Alpha, the second Beta and so on. In 1922, the International Astronomical Union standardized the naming of celestial objects including constellations However, several different conventions are in use. First seen in Historia Coelestis Britannica in 1712, Flamsteed's Numbers assigns a number to a star that represents its right ascension.

Telling Tales

• When our ancestors first grouped stars together they did so as a means to understand the world around them. They chose images of animals, such as the Scorpion, and mythical beings, like Perseus, that existed in their own societies and mapped them against the shapes formed by stars in the night sky. They used the images to tell stories, believing, for example, that they depicted great battles between gods. Orion the Hunter was thrown into the stars by his grieving lover Diana after she had been fooled into killing him by her brother Apollo. Before the written word, the use of constellations as story-telling devices ensured that beliefs central to many early civilizations were passed on to succeeding generations.